This invention relates generally to broadband communications systems, such as cable television systems, and the electronic devices used in such systems, and more specifically, to housings that enclose the electronic devices.
A communication system 100, such as a two-way cable television system, is depicted in FIG. 1. The communication system 100 includes headend equipment 105 for generating forward signals that are transmitted in the forward, or downstream, direction along a communication medium, such as a fiber optic cable 110, to an optical node 115 that converts optical signals to radio frequency (RF) signals. The RF signals are further transmitted along another communication medium, such as coaxial cable 120, and are amplified, as necessary, by one or more distribution amplifiers 125 positioned along the communication medium. Taps 130 included in the cable television system 100 split off portions of the forward signals for provision to subscriber equipment 135, such as set top terminals, computers, and televisions.
The system 100 also has reverse transmission capability so that signals, such as data, video, or voice signals, generated by the subscriber equipment 130 can be provided in the reverse, or upstream, direction to the headend 105 for processing. The reverse signals travel through the taps 130 and any nodes 115 and other cable television equipment, e.g., reverse amplifiers, to the headend 105. In the configuration shown in FIG. 1, RF signals generated by the subscriber equipment 135 travel to the node 115, which converts the RF signals to optical signals for transmission over the fiber optic cable 110 to the headend 105.
It is known that electronic devices, such as an amplifier or optical node, generate a significant amount of heat during operation. As a result, much time is taken in the design of the electronic devices to compensate for the heat generation. One example is the design of the housings that enclose the electronic devices. Conventional housings include such features as a substantial amount of metal, for example, aluminum, and fins that are formed into the metal housing to radiate the heat outward away from the internal electronics. Consequently, in addition to the housing being very costly, the weight due to the amount of metal causes stress and wind shears on the coaxial cable, since the amplifiers are typically mounted on coaxial cable and cable strands between poles. Cost and weight are two factors used by the operators when designing a cable television system, and if either one is too high, adjustments within the design need to be made.
A radio frequency (RF) cable amplifier housing is shown in FIG. 2 and is also shown in U.S. Pat. No. Des. 409,612, the teachings of which are incorporated herein by reference. Metal housings have been used since the conception of cable television electronic equipment due to the significant heat that is generated from the internal electronic devices. Conventional plastics used in housings for other electronic devices, such as cellular telephones, and even metal housings without fins, have not been able to withstand the heat generation from the internal components of the devices used in the cable television industry. There are, however, many disadvantages to the metal housing. The costs associated with casting the housings are high due the amount of metal that is used. Fins, which are added to the housing to increase the heat dissipation, greatly increase the material and manufacturing costs. Additionally, if harsh environmental conditions require added protection, such as an epoxy coating or a powder coating, the costs are increased even more.
In some applications, the housings exposed to harsh environments, such as salt, sand, and wind, may adversely affect the housing and, potentially, the electronic device within the housing. A typical application for an electronic device within the cable television system 100 is mounting the housing that encloses the electronic device on aerial cable 120. Some of the aerial cable 120 may be located directly along beachfront property. The combination of salt, sand, water, and wind may decrease the life of the housing. An epoxy coating is sometimes used to cover the housing to enhance the corrosion resistant properties; however, when the housing is exposed to harsh elements for a period of time, the coating may begin to pit and the metal may corrode. Additionally, the hardware, such as bolts and springs, used that closes the housing may freeze within the sockets, thereby not allowing the housing to open without breaking the hardware. Also, if the housing corrodes around a carbon-based, rubber gasket that encircles the inside of the housing for weatherproofing, there is risk of damage to the gasket and the internal electronics.
In summary, the housing for an electronic device has conventionally been made from metal, which results in a very heavy and costly housing. Epoxy or powder coatings that are sometimes used to cover the housing and allow it to withstand harsher weather conditions and enhance the heat dissipation, also dramatically increase the cost of the housing. Thus, what is needed is a low-cost housing that withstands severe environments without corrosion while dissipating the heat that is generated within the housing.